The present invention relates to an ignition system for an internal combustion engine, or more in particular to an ignition system for an internal combustion system comprising a semiconductor power switching device, in which the ignition coils are prevented from being heated by detecting a breakdown by shorting of the semiconductor power switching device.
A conventional ignition system using a semiconductor power switching device, such as a power transistor, is widely known as disclosed in JP-A-60-209667.
According to this prior art system, the primary current of sequentially-connected ignition coils is detected by a common current detection circuit for constant-current control.
In this prior art system, even though the primary current of the ignition coils is controlled below a predetermined value, a continuous current could flow in the ignition coils and the coils could be burned by being heated thereby to generate smoke or combustion of the exterior resin of the ignition coils if the power switching device were to break down due to shorting.